Despite the widespread use of efficacious antiretroviral therapies, HIV-associated neurocognitive disorders (HAND) remain highly prevalent. Converging lines of evidence implicate dopaminergic dysfunction in HAND as well as in substance abuse disorders, a common comorbidity in individuals with HIV. In preliminary studies of an HIV cohort, we have shown evidence of genetic associations between dopaminergic genes and cognition; these associations are influenced by substance use status. It is the overarching hypothesis of this project that due to chronic, tonic changes in dopaminergic neurotransmitter tone, neurobiological processes affecting this circuitry and leading to cognitive impairment diffe between substance users and non-users, despite phenotypic similarities of HAND in both populations. In this award, I will be combining genetic techniques with gene expression analyses and cognitive assessments to more carefully assess the distinct differences between substance and non-substance users within an ethnically diverse HIV-positive population. Specifically, I will fully study the two main genes of interest, dopamine D1 receptor and dopamine D2 receptor (DRD1 and DRD2, respectively), using next-generation sequencing technologies in 100 newly recruited HIV-infected individuals with and without HAND, and with and without substance abuse as well as an additional 300 subjects obtained from resources within the National NeuroAIDS Tissue Consortium. In a subset of patients, I will examine brain expression levels of DRD1 and DRD2 using both traditiona methods (in situ and/or qRT- PCR) to determine potential functional roles of newly identified mutations. To fully query the whole transcriptome, RNA-sequencing technologies will be used to determine the differences between individuals with and without HAND, and with and without substance abuse. Together, this project will allow an in-depth study into both dopaminergic dysfunction as well as the underlying neuropathogenesis affected by both HIV and substance use.